The difference between art and design is that design serves a concrete purpose. Obviously there is creativity involved in designed, but the creativity of a good designer is about solving problems. This manifests in different ways, but for interactive or industrial design usability is the most important concern, and therefore, all else being equal, uniformity across sites is a good thing. Forms of visual design whose primary concerns are either/or attention-grabbing (eg. billboards, posters) or communication (eg. magazine, flyers) naturally enjoy a bit more creative leeway.

With established norms stabilizing on the web, UI creativity there can and should decrease. However that said, there is always the possibility for optimizing towards narrower and more specific problems, but this must be done sparingly since new interactive paradigms introduct a cognitive load on the user which may not be acceptable for the intended audience.

Well in terms of layout and functionality, sure, I understand the need for consistency. My comment was referring to the artistic element of color schemes and fonts. That is the part that gets annoying when everybody does it the same. You can have consistency of function while being creative with colors and things like that. I love it when I show up on a site with bold colors and unique design ideas. It gives me the impression that the company is willing to try new things.

Maybe you're just annoyed everyone is using Twitter Bootstrap?

It's not just Bootstrap, though, is it? It's also flat design, similar colour palettes, similar fonts, using one big hero image or some sort of carousel, and numerous other details.

And the real kicker is that most of these aren't done well.

Aside from having a very limited expressive range, flat design has all kinds of usability problems that plenty of people have called out from the start. The fact that both Microsoft and Apple have chosen to adopt flat design does not change that unfortunate reality.

I cringe a little every time I see a web site using Proxima Nova, a font which renders horribly at many sizes and in many browsers, whatever all the renting-you-fonts-for-money services will tell you about how optimised their fonts are. I wince even more when I have to use a site with trendy thin fonts that are so hard to read under many conditions that I have to start hacking the CSS around to make it more comfortable. At least there is a small silver lining here: Helvetica is less common in font stacks now, so everyone on Windows who has printer fonts installed can breathe a sigh of relief.

Carousels have problems that are well known to anyone who studies usability, yet people persist in using them, presumably because they care more about looking cool in a demo than having a site that is actually effective. Or they just don't know any better, because they don't know anything about usability, and anyway they feel compelled to use at least 98% of what's in their template on every project. After all, the only acceptable alternative is to use a hero image that automatically scales to full page width, thus reducing modern, good quality, high resolution monitors to displaying heavily pixellated versions of clip art that is probably irrelevant anyway, and obviously no designer would do something silly like that.

It's not the consolidation and uniformity that bothers me. It's consistently doing things that just aren't very good that I find frustrating.

Uniformity in user interfaces is an emergent property when many website owners optimize for UI ease of use. Who would want to sacrifice pageviews, conversion rates, purchases for non-standard interfaces? Also Bootstrap is very easy to use and solves the problem for website owners and users.

Could be a founder principle: A few successful Web sites use a given UI approach, people get used to that, so new Web sites copy approach to minimise learning time. Couple that with Bootstrap's availability.

Example: Windows 95, 98, ME, and XP all had a panel at the bottom with a menu ('start') button on the left. That became normal for a computer. Anything different (Canonical's Unity, Gnome's Gnome-Shell) is seen as 'problematic'.

Reference: Zen and the Art of Motorcycle Maintenance, the bit about the early history of motorbikes and the surprising range of arrangements.

The Windows taskbar and start menu allow for certain levels of usability and efficiency.

The approaches offered by newer systems like Unity, GNOME Shell, and Windows 8 all fall well, well below these levels set by the earlier approaches, however.

They're seen as "problematic", to use your terminology, because they are inherently inferior to earlier approaches in many important ways. They leave users worse off. So of course they will be seen in a negative light.

The Windows taskbar was radically changed in 7 to turn it into a dock rather than an active windows bar. And the start menu was radically changed twice - the transition to Vista, where they added semantic search, and in 8 when they made it pretty much only semantic search.

I'm confused how that makes Unity "well below these levels" since their meta-key function is effectively a more robust search and their taskbar is a dock, that is just on the side of your screen.

Or Gnome, where their meta functionality is, again, search. And their dock just requires you to hit meta to access, as if its always hidden. And you get window presentation that way.

The only significant loss - and I would agree it is significant, maybe its one of the reasons I use KDE - is the lack of a categorized tree graph of all installed programs, for when you don't know what you want, you don't have it pinned, and need a way to narrow your options down. That doesn't happen easily in Gnome or Unity (you can present applications by group by searching the group) but a novice user wouldn't know that.